The present invention relates to scales for weighing fluids, and more particularly to a filter for stabilizing the readout of scales that dynamically monitor the changing volume of fluid in a fluid receptacle utilized for surgical procedures.
Various surgical procedures require the introduction and withdrawal of fluids from the human body, e.g., for the purposes of insufflation to permit endoscopic surgery or for providing a lavage of a surgical site to draw off blood, and/or morcellated tissues for maintaining an acceptable level of visibility and/or sterility at the surgical site. In such procedures, great care must be taken to maintain an acceptable rate of fluid input and output, e.g., to maintain a suitable fluid volume and pressure within the body while, at the same time, maintaining an acceptable level of fluid throughput to accomplish the objectives of its introduction. Present fluid management systems frequently utilize scales from which fluid receptacles are hung to monitor the rate of fluid input and output. More particularly, a fluid receptacle for fluid that is being pumped into the body will register a loss in weight over time at a rate directly proportional to the rate of volume change as the fluid is evacuated from the receptacle and is pumped into the body. Similarly, fluid receptacles that receive fluids withdrawn, leaking or otherwise expelled from the body will gain weight in proportion to the rate of fluid volume acquisition. In this manner, the rate of fluid transfer to and from the body can be measured, monitored and controlled.
Surgical fluids are typically contained in disposable plastic bags, bottles, buckets or other containers that are hung by an attached tab, bracket or other suspender from a hook that depends from a scale. Accordingly, the fluid receptacle hangs from the scale hook and is free to oscillate in a pendulous manner until it comes to rest naturally, i.e., due to friction and other dampening forces. Because the fluid receptacle is free to oscillate, the weight readout on the scale from which the container is hung oscillates correspondingly. That is, when the weight swings through its range of motion, it displays the variations in weight associated with pendulous motion, e.g., lightest at the two extremes of elevation and heaviest at its nadir. Because a hanging fluid receptacle typically has a hanging apparatus that permits the receptacle to oscillate in many planes, the fluid receptacle executes a compound motion having pendulous and rotary components, i.e., the bottom of the receptacle is free to trace a circle while at the same time swinging pendulously. Accordingly, depending upon the forces imparted to the fluid receptacle, the periodic motion and the corresponding oscillation of the measured weight vary. From the standpoint of the surgical team, it is beneficial to have an accurate readout of the fluid receptacle weight (and associated rate of fluid infusion or suction that may be derived therefrom) at all times. It is therefore beneficial to minimize the time for stabilization of the hanging fluid receptacle. More particularly, it has been noted that the fluid receptacle can take several seconds to stabilize when first hung on the scale. Since the fluid receptacle is subject to being moved at any time, e.g., due to someone brushing up against it, moving the scale or tugging on the hoses attached to the receptacle during the surgical procedure, the weight readout and associated flow rate information can be disturbed at any time by these events. Accordingly, it would be desirable to have a fluid management system that displays a more stable fluid weight readout and one which stabilizes more rapidly after having been disturbed. It is therefore an object of the present invention to provide same.
The problems and disadvantages associated with the conventional techniques and devices utilized to monitor fluid dispensing and retrieval during surgery are overcome by the present invention which includes a scale system for measuring the weight of an object. The scale system has a support for holding the object and a transducer coupled to the support for converting a force exerted thereon by the object into an electrical signal. A filter receives the electrical signal from the transducer and suppresses noise in the signal at selected frequencies.